Specific Aims of this protocol are to 1)test the hypothesis that BBS carriers have a characteristic retinal phenotype by ERG; 2)determine the usefulness of ERG as a diagnostic test for distinguishing carriers and non-carriers in at-risk BBS families by calculating positive and negative predictive values, sensitivity, and specificity; 3) determine whether the ERG abnormalities of BBS carriers are associated with, or predictors of age-dependent visual problems; and 4) use the ERG's and genotypes of unaffected family members to identify genetic recombinants that can be used to narrow the critical region of the BBS disease gene in Boston area Puerto Rican families.